The present invention generally relates to a modular x-ray phantom system. More particularly, the present invention relates to a modular x-ray phantom system comprising a plurality of interchangeable phantoms and a modular phantom carrier.
X-ray systems, such as an image intensifier, storage phosphor plates or digital detectors, typically include an x-ray emitter and an x-ray receiver. A target to be viewed, such as a human body, is arranged between the x-ray emitter and the x-ray receiver. X-rays produced by the emitter travel through the target to reach the receiver. As the x-rays travel from the emitter through the target, internal components of the target may decrease the energy of the x-rays to varying degrees through effects such as the blocking or absorption of some of the x-rays. The blocking or absorption of x-rays within the target causes the received x-ray energy levels to vary. The x-ray receiver receives the x-rays which have traveled through the target. An image of the target is generated at the x-ray receiver. The image produced at the receiver contains regions of light and dark which correspond to the varying intensity levels of the x-rays which have passed through the target.
The x-ray images may be used for many purposes. For instance, internal defects in the target may be detected. Additionally, changes in internal structure or alignment may be determined. Furthermore, the image may show the presence or absence of objects in the target. The information gained from x-ray imaging has applications in many fields, including medicine and manufacturing.
In order to help ensure that x-ray images may be used reliably, it is advantageous to calibrate x-ray systems. The calibration of x-ray systems is important for several reasons, including image quality. Poor image quality may prevent reliable analysis of the x-ray image. For example, a decrease in image contrast quality may yield an unreliable image that is not usable. Additionally, the advent of real-time imaging systems has increased the importance of generating clear, high quality images. The calibration of x-ray systems may help to produce a distinct and usable representation of the target.
The calibration of x-ray systems is also important for safety reasons. For example, exposure to high levels of x-ray energy may involve some health risk to humans. Because of the health risk, governmental standards are set for the use of x-ray systems. The level of x-ray energy emitted by an x-ray system may be measured in terms of radiation dosage. Calibration of x-ray systems may ensure that the radiation dosage to which the target is exposed does not exceed regulatory standards.
One device that may be used in the calibration of x-ray system parameters, such as image quality and radiation dosage, is an x-ray phantom. Several types of phantoms exist, including physical replica phantoms and physics-based phantoms. For example, a physical replica phantom may be a physical replica of an x-ray target, such as a human body part. A physics-based phantom may be comprised of various structures affixed to a common base. The structures of a physics-based phantom may possess varying characteristics, such as shape, size, density, and composition. Furthermore, the structures of physics-based phantoms may be constructed from various materials, including metal and plastic.
The structures of physics-based phantoms may affect the intensity of the x-rays which pass through the physics-based phantom. For example, metal structures may block some or most of the x-rays. Additionally, plastic structures may merely provide minimal attenuation of the x-rays. A pattern resulting from the changes in the intensity of received x-rays is represented in an x-ray image. The resulting pattern in the x-ray image may be easy to detect and analyze due to factors such as the contrast produced by the difference in received x-ray intensities.
Currently known phantoms may serve a variety of purposes. For example, phantoms may test performance parameters of the x-ray system. Also, phantoms, combined with radiation probes, may be used to gauge the radiation dosage of x-ray energy emitted by the emitter. Furthermore, phantoms may be used for calibration and image quality assessment.
Typically, physics-based phantoms may be designed to measure one or more parameters of an x-ray system. Different phantoms may produce different patterns of x-ray intensity or attenuation. The different patterns of x-ray intensity or attenuation may be used to measure or test different performance parameters of the x-ray system. Thus, multiple phantoms may be necessary to measure a plurality of x-ray system parameters.
However, the use of multiple phantoms in an x-ray system may introduce unwanted variance in x-ray system calibration. For instance, the use of multiple phantoms in an x-ray system may introduce variance in the positioning of the phantom as a result of factors such as variation in phantom size and configuration. Variation in the positioning of the phantom may yield variation in the x-ray image. Variation in the x-ray image may result in loss of accuracy in x-ray system calibration. However, positioning of the phantom in a consistent location in the x-ray field may assist in reliable and consistent measurement of parameters, such as image quality and radiation dosage, on x-ray systems.
Consistent positioning of the phantom also may assist in providing trending data for x-ray system parameters. Trending is known as the comparison of x-ray system parameters over time to establish a trend of x-ray system parameters. Tracking of trending may be important to evaluate the performance of the x-ray system over time.
Often, a phantom carrier is used to position a phantom in an x-ray system. As previously mentioned, each x-ray system has an x-ray receiver. The x-ray receiver has an aperture through which the x-rays are received. The characteristics of the aperture, such as size, may vary depending upon the x-ray system being used. A modern phantom carrier comprises an x-ray phantom embedded in a frame. The phantom carrier serves to position the phantom in the path of the x-ray energy received through the aperture.
Due to the variance in the characteristics of apertures (such as size) in different x-ray systems, a phantom carrier may be specific to the aperture of the particular x-ray system. Thus, to provide calibration of x-ray systems with different apertures, a plurality of phantom carriers may be required.
A physics-based phantom carrier is described in U.S. Pat. No. 5,841,835 issued to Aufrichtig et al. ("Aufrichtig"). The phantom embedded in the Aufrichtig phantom carrier may be used in the calibration and standardization of digital x-ray fluoroscopy and radiography systems. The Aufrichtig phantom carrier positions the embedded phantom in the path of the x-ray beam. The Aufrichtig phantom carrier is a single piece, integrated phantom carrier with an embedded phantom.
Characterizing the performance of an x-ray system may require multiple phantoms embedded in multiple carriers to measure differing x-ray system parameters. Currently, the use of multiple phantom carriers in an x-ray system may introduce problems, such as variance in positioning, similar to those discussed above with the use of multiple phantoms. Variance in phantom carrier design or positioning may introduce spatial variation in measurement and trending of x-ray system parameters.
Additionally, the manufacture of multiple phantom carriers may be very labor intensive due to factors such as variation in design and customization. The manufacture of multiple phantom carriers may also be expensive due to factors such as material cost and production time. The multiple integrated phantom systems may also require a large amount of storage space.
Thus, a need has long existed for an x-ray phantom system that may be transferred easily between a plurality of x-ray systems. A need exists for an x-ray phantom system which may allow a phantom to be repeatedly positioned within an x-ray system with minimal spatial variance, thus increasing the accuracy of x-ray system calibration. Additionally, a need exists for an x-ray phantom system which may allow a plurality of phantoms to be repeatedly and reliably positioned in an x-ray system. A need also exists for an x-ray phantom system which may allow a phantom to be easily transferred among a plurality of x-ray systems with different apertures. In addition, a need exists for an x-ray phantom which may allow more accurate calibration of x-ray systems and may allow measurement of additional parameters.